The use of reed valves in engine passages to control the back-flow of fluids is known. A reed valve can be located in an intake passage leading to a cylinder to obstruct back-flow of fluids out of the cylinder into the intake passage.
A reed valve typically includes a cage which spans the cross section of the engine passage. The cage has one or more cage ports allowing fluid flow through the cage. A petal consisting of a flat, flexible member is pivotably connected to the downstream side of the cage adjacent the cage port so that the petal covers the port. Fluid flow having sufficiently high pressure upstream of the cage causes the petal to deflect away from the cage allowing fluid flow therethrough. The petal obstructs fluid back-flow from downstream of the cage toward it since such fluid back-flow will force the petal against the cage obstructing the cage port.
The length of the petal can affect the improvements in engine performance produced by the reed valve and the engine speeds at which the improvements are produced. In typical reed valves, the length of the petal is fixed. This can limit the improvements in engine performance produced by the reed valve and the range of engine speeds at which the improvements are produced.